In a place where the AC runs ten or more months a year, the ductwork moves a lot of air. Along with that air comes dust, pet hair, construction debris from past renovations, and in humid conditions, the moisture that helps all of it stick.
Dirty ducts and registers can make a home feel stuffy, spread dust back into rooms right after you clean, and make allergies worse. When the evaporator coil and drain are also dirty, airflow drops and the system works harder to deliver the same cooling.
That's why we treat duct cleaning and AC maintenance as one visit: clean the ducts and registers, clean the coils, flush the condensate drain, replace the filter, and check the electrical and refrigerant side while we're there. You end up with cleaner air and a system that isn't fighting its own dirt.
For most homes, a full duct cleaning every few years is reasonable, with coil and drain maintenance at least once a year. Homes with pets, recent renovations, or anyone with allergies may benefit from cleaning more often.